Add marker to 2D tracking list via clip.stabilize_2d_add() or other means
You can add and adjust tracking markers without using operators.

Each movie clip has a tracking property which has a list of the tracks that have markers.

Every tracking.track is a point in that you are tracking. The markers for each track are keyframes of the tracks location.

import bpy

track_data = bpy.data.movieclips['movie_track'].tracking

for i in range(10):
    # this adds a new point to be tracked
    trck = track_data.tracks.new()
    for f in range(1,100,10):
        # this sets the location of the point at frame f
        x = (f+i) * 0.1
        y = (f+i) * 0.1
        trck.markers.insert_frame(f, co=(x,y))

# get track data
for t in track_data.tracks:
    for m in t.markers:
        print('marker on frame {} at {}'.format(m.frame, m.co))